Brake pedal device

ABSTRACT

In a brake pedal apparatus ( 50 ) of the invention, an engagement condition between an engagement means ( 15 ) and an L-shaped member ( 43 ) is maintained and a second lever member ( 2   a   2 ) pivots with a second pivot shaft ( 13 ) being the center, setting a small lever ratio, if a pedal force (F p ) is equal to or less than a set value (F p0 ) when a brake pedal ( 2 ) is depressed while the engaging means ( 15 ) and the L-shaped member ( 43 ) are in the engagement condition. If the pedal force (F p ) exceeds the set value (F p0 ), the engagement between the engaging means ( 15 ) and the L-shaped member ( 43 ) is cancelled, and the engaging means ( 15 ) moves while causing the L-shaped member ( 43 ) to pivot. An engaging-and-connecting lever ( 45 ) disengages from a linear portion ( 43   b ), and the engaging-and-connecting lever ( 45 ) pivots so that its latch pawl latches onto teeth ( 47   a ) of the second lever member ( 2   a   2 ), joining the first and second lever members ( 2   a   1 ), ( 2   a   2 ) unitarily. Thereby, a lever ratio is changed, and a large lever ratio is set.

BACKGROUND ART

The present invention relates to the technical field of brake pedalapparatus for inputting an operator's operating force for the purpose ofbraking with a brake apparatus, and more particularly to the technicalfield of brake pedal apparatus in which the pedal ratio is variable.

With brake systems for vehicles such as automobiles, a brake is oftengenerally actuated by a force for depressing a break pedal.

FIG. 5 is a view for schematically showing the basic structure of aconventional break apparatus for general use with such a brake pedal.FIG. 5 shows the following: numeral 1 denotes a brake apparatus; numeral2 denotes a brake pedal for performing a brake operation; numeral 2 arepresents a lever; numeral 3 denotes a booster for boosting a pedalforce of the brake pedal 2 by the power of liquid pressure, negativepressure, or air pressure (positive pressure) for outputting it; numeral3 a denotes an input shaft of the booster 3; numeral 4 denotes atandem-type master cylinder (hereafter also referred to as “MCY”) thatis actuated by the output of the booster 3 to generate a master cylinderpressure; numerals 5 and 6 denote wheel cylinders (hereafter referred toas “WCY”) for a first brake system, to which an MCY pressure of the MCY4 is supplied as a brake pressure to generate a brake force; numerals 7and 8 denote WCYs for a second brake system, to which the MYC pressureof the MCY 4 is supplied as a brake pressure to generate a brake force;and numeral 9 denotes a reservoir of the MCY 4.

In this brake apparatus 1, the input shaft 3 a of the booster 3 movesforward (moves leftward in FIG. 5) by depression of the brake pedal 2,and the booster 3 boosts the pedal force and outputs it. The output ofthe booster 3 causes the MCY 4 to generate the MCY pressure, and the MCYpressure is respectively supplied to each of the WCYs 5, 6, 7, and 8,whereby a brake is operated with a great force resulting from theboosted pedal force.

In a brake apparatus 1 as described above, a pedal ratio (L1+L2)/L1 ofthe lever 2 a of the brake pedal 2 is typically in many casesinvariable. Here, L1 represents the distance between the pivot centerpoint of the lever 2 a and the connection point at which the input shaft3 a of the booster 3 is connected to the lever 2 a, and L2 representsthe distance between this connection point and the center point of thebrake pedal 2.

When the pedal ratio is invariable as described above, the followingproblems arise.

(1) The pedal force becomes large when the boost power failure of thebooster 3 occurs (for example, at the time of power source failure).

(2) Depending on circumstances, there are cases in which the pedalstroke becomes large, resulting in unsuitable feel.

(3) In emergency braking, there are cases in which a large brake forcecannot be produced by beginners or the like.

(4) At the time of vehicle collision, there are cases in which the brakepedal moves toward driver's side greatly.

(5) When attempting to set the brake pad at a large space from a brakedisk or a brake drum in order to improve fuel economy by preventing thedragging of W/C (although a very large space cannot be made since it isnecessary to take into account the stroke loss of the brake pedal 2),the pedal stroke becomes larger accordingly.

In view of this, JP-A-2002-347590 proposes a brake pedal apparatus thatcan solve the foregoing problems by making the pedal ratio variableeasily. FIG. 6 schematically shows the brake pedal apparatus disclosedin JP-A-2002-347590, wherein (a) is a front view similar to FIG. 5 and(b) is a partially-enlarged view showing the state immediately after thepedal ratio has been varied. It should be noted that the brake apparatus1 shown in FIG. 5 is also disclosed in JP-A-2002-347590, so in the brakeapparatus 1 equipped with a brake pedal apparatus 50, which is shown inFIGS. 6(a) and 6(b), the same elements as those of the brake apparatus 1shown in FIG. 5 are designated by the same reference numerals and thedetailed description thereof will be omitted. Although some of theelements in the brake apparatus 1 shown in FIG. 5, such as the MCY 4,the WCYs 5, 6, 7, and 8, and the reservoir 9 are not shown in FIG. 6(a),the brake apparatus 1 shown in FIG. 6(a) is, of course, also furnishedwith these elements.

Further, FIGS. 6(a) and 6(b) show the following; numeral 2 a ₁ denotes afirst lever member provided pivotably onto a bracket 10 a attached onthe vehicle body 10 (for example, on a toe board) with a first pivotshaft 11; numeral 2 a ₂ denotes a second lever member, on one end (thelower end) of which the brake pedal 2 is provided and the other end (theupper end) of which is connected-relatively pivotably to one end of thefirst lever member 2 a ₁ (the left end that is further leftward than thefirst pivot shaft 11) with a second pivot shaft 13; numeral 2 a ₄denotes a third lever member, one end (the lower end) of which ispivotably connected to the bracket 10 a by a shaft 37 and the other end(the upper end) of which is relatively pivotably connected to an inputshaft 3 a of the booster 3 by a shaft 38; numeral 2 a ₅ denotes a fourthlever member that connects the mid portion of the second lever member 2a ₂ (the portion closer to the brake pedal 2 than the location of thefirst pivot shaft 11) to a mid portion of the third lever member 2 a ₄with two shafts 2 a ₇ and 2 a ₆; numeral 2 a ₈ denotes a stop portionthat is provided for the second lever member 2 a ₂ and is abuttable ontothe first pivot shaft 11; numeral 15 denotes a pin-shaped engaging meansprovided to the other end of the first lever member 2 a ₁ (the right endright to the first pivot shaft 11); numeral 39 denotes an arc-shapedmember made of a rigid body, one end of which is pivotably supported onthe bracket 10 a by a pivot shaft 42 and which has an arc-shaped surface39 a onto which the engaging means 15 abuts at all times; numeral 40denotes a spring provided in a contracted state between the other end ofthe arc-shaped member 39 and the bracket 10 a in such a manner that iturges the arc-shaped member 39 clockwise in FIGS. 6(a) and 6(b) at alltimes; and numeral 41 denotes a retaining portion composed of a V-shapedgroove, which is provided to the arc-shaped member 39 and into which theengaging means 15 can engage.

When in an inoperative condition, the thus configured brake pedalapparatus 50 shown in FIGS. 6(a) and 6(b) is kept in a state in whichthe engaging means 15 is engaged in the retaining portion 41 by thespring force of the spring 40, and the stop portion 2 a ₈ abuts on thefirst pivot shaft 11, which is shown in FIG. 6(a).

When the brake pedal 2 is depressed in a normal manner from thisinoperative condition, the pedal force F_(p) does not reach a set valueF_(p0), that is, a pedal-ratio change condition is not established. Forthis reason, the second lever member 2 a ₂ is caused to pivot clockwisein FIG. 6(a) with the connection shaft 2 a ₇ being the center, and as aconsequence, the second lever member 2 a ₂ causes the first lever member2 ^(a) ₁ to pivot clockwise via the second pivot shaft 13, with thefirst pivot shaft 11 being the center. However, since this pivot forceof the first lever member 2 a ₁ effected by the second lever member 2 a₂ is small, the engaging means 15 does not disengage from the retainingportion 41 and is kept engaged in the retaining portion 41. Accordingly,the first lever member 2 a ₁ does not pivot and only the second levermember 2 a ₂ pivots clockwise in FIG. 6(a), with the second pivot shaft13 being the center. Consequently, the third lever member 2 a ₄ pivotscounterclockwise via the fourth lever member 2 a ₅, with the shaft 37being the center, and the input shaft 3 a strokes forward, actuating thebooster 3, whereby a normal brake is operated. When releasing the brakepedal 2, each of the lever members 2 a ₄, 2a ₅, and 2 a ₂ pivots in anopposite, inoperative direction, and the brake pedal apparatus 50 entersan inoperative condition shown in FIG. 6(a), whereby the normal brake isreleased.

For example, when the brake pedal 2 is depressed more strongly thanusual because of emergency braking or the like, the pedal force F_(p) isthe set value F_(p0) or higher; that is, the pedal-ratio changecondition is established. Accordingly, since the pivot force of thefirst lever member 2 a ₁ effected by the second lever member 2 a ₂ isgreat, the engaging means 15 disengages from the retaining portion 41,as shown in FIG. 6(a), and the first lever member 2 a ₁ pivots clockwisein FIG. 6(b), with the first pivot shaft 11 being the center, and thesecond lever member 2 a ₂ pivots in the same direction, with theconnection shaft 2 a ₇ being the center.

At this time, the engaging means 15 shifts from the abutting surface ofthe V-shaped groove of the retaining portion 41 to the abutting surfaceof the arc-shaped member surface 39 a of the arc-shaped member 39, whileabutting against the abutting surfaces such that the contact angle(specifically, the contact angle with the first lever member 2 a ₁ andthe arc-shaped member 39) does not change continuously but changesabruptly. In addition, since the pivot amount of the first lever member2 a ₁ is greater than that of the second lever member 2 a ₂, the firstpivot shaft 11 immediately abuts, at the beginning of the pedaldepression, onto the stop portion 2 a ₈ of the second lever member 2 a₂, which is slightly spaced from the first pivot shaft 11, resulting ina balanced position between the first lever member 2 a ₁ and the secondlever member 2 a ₂. Thereafter, the first lever member 2 a ₁ and thesecond lever member 2 a ₂ pivot unitarily with the first pivot shaft 11being the center. Thus, the pedal ratio is changed into a greater pedalratio than that at the time of normal pedal depression. That is, the MCYpressure has so-called inverse two-stage characteristics in which as thepedal force F_(p) increases, the MCY pressure increases with a greaterboosting ratio than that in conventional ones.

When the pedal force F_(p) is the set value F_(p0) or higher, at thetime of boosting power failure by the booster 3 as well, the pedal ratiois likewise changed to be greater. Therefore, the MCY pressure linearlyincreases to a much greater value than it conventionally increases inaccordance with the increase of the pedal ratio, assisting the brakeforce.

Furthermore, the pedal stroke-pedal ratio profile of this brake pedalapparatus 50 shows the characteristics as follows. When the engagingmeans 15 is in a state in which it is engaged with the retaining portion41, the pedal ratio is considered mostly invariable, although the pedalratio slightly decreases initially and thereafter slightly increaseswith respect to the increase in the pedal stroke, as shown in FIG. 7(a). On the other hand, when the engaging means 15 is disengaged fromthe retaining portion 41, the pedal ratio increases in accordance withthe increase in the pedal stroke, as shown in FIG. 7(b).

Since this brake pedal apparatus 50 has two lever members, the thirdlever member 2 a ₄ and the forth lever member 2 a ₅, the brake pedalapparatus 50 can be disposed under the input shaft 3 a of the booster 3,as shown in FIG. 6(a). Thereby, freedom in arrangement of the pedalapparatus 50 improves, and the total length of the assembled body of thepedal apparatus 50, the booster 3, and the master cylinder 4 can beshortened.

Nevertheless, in the conventional brake pedal apparatus 50 shown in FIG.6(a), the pin-shaped engaging means 15 is engaged with the V-shapedgroove of the retaining portion 41, and therefore, a considerably largefriction force is produced between the engaging means 15 and theretaining portion 41 when the pedal-ratio change condition isestablished and the engaging means 15 is disengaged from the V-shapedgroove of the retaining portion 41. It is desirable that the frictionforce should be reduced as much as possible and thereby the pedal ratiois changed smoothly to obtain a better pedal feel.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a brake pedal apparatus thatmakes it possible to change the pedal ratio easily and more smoothly toobtain a better pedal feel.

In order to achieve the foregoing object, a brake pedal apparatus of theinvention comprises: a first lever member whose mid portion is pivotablysupported on a vehicle body by a first pivot shaft; a second levermember having a pedal on an end thereof and being relatively pivotablyconnected to an end of the first lever member by a second pivot shaft,to which an input shaft of a booster or of a master cylinder ispivotably coupled; a pivot-inhibiting control means for controllingpivoting of the first lever member so that the first lever member isinhibited from pivoting when a predetermined condition is notestablished while the first lever member is -permitted to pivot when thepredetermined condition is established; and a joining means for causingthe second lever member to pivot together with the first lever member,with the first pivot shaft being a pivot center, when the first levermember is permitted to pivot, the brake pedal apparatus characterized inthat: the pivot-inhibiting control means comprises an engaging meansprovided on the first lever member, and a shift-inhibiting control meanshaving an abutting surface onto which the engaging means abuts and beingfor inhibiting the engaging means from shifting so as to keep itsengagement with the engaging means when the predetermined condition isnot established, and for permitting the engaging means to shift so as tocancel its engagement with the engaging means when the predeterminedcondition is established; and the abutting surface of theshift-inhibiting control means is an abutting surface whose shape doesnot change abruptly.

In addition, the invention is characterized in that: the joining meansincludes a catch member provided on the first lever member and aconnecting member provided on the second lever member and beinglatchable onto the catch member; and the connecting member is configuredto be controlled by the shift-inhibiting control means so that it doesnot latch onto the catch member when the predetermined condition is notestablished while it latches onto the catch member when thepredetermined condition is established.

Further, the invention is characterized in that: the catching member hasa predetermined number of tooth (teeth) or groove(s), and the connectingmember is provided pivotably on the second lever member and includes anengaging-and-connecting lever having a latch pawl being latchable withthe tooth (teeth) or the groove(s); and the engaging-and-connectinglever is controlled by the shift-inhibiting control means so that theengaging-and-connecting lever is set at a position such that the latchpawl does not latch with the tooth (teeth) or groove(s) when thepredetermined condition is not established, while theengaging-and-connecting lever is set at a position such that the latchpawl latches with the tooth (teeth) or groove(s) when the predeterminedcondition is established.

With the thus-configured brake pedal apparatus according to theinvention, the abutting surface of the shift-inhibiting control meansagainst the engaging means is formed so as not to change-abruptly;therefore, the resistance (friction) caused by the shift of the engagingmeans can be reduced when the engagement relation is cancelled betweenthe engaging means and the shift-inhibiting control means when the pedalratio changes. Accordingly, the cancellation of the engagement relationbetween the engaging means and the shift-inhibiting control means, thatis, the pedal ratio change, can be smoothly performed. Thereby, thepedal feel associated with the change in the pedal ratio can be improvedfurther than a conventional pedal feel.

Moreover, with the brake pedal apparatus of the invention, the firstlever member and the second lever member are unified by controlling theconnecting member with the shift-inhibiting control means that canreduce the friction caused by the shift of the engaging means.Therefore, the contact noise produced at the time of unification of thefirst lever member and the second lever member can be prevented, and thepedal -ratio when the first and second lever members are unified can beset nearly at a desired pedal ratio. Thereby, pedal feel can be improvedfurther.

Moreover, the brake pedal apparatus of the invention makes it possibleto change the pedal ratio with a simple structure because the connectingmember is structured by the engaging-and-connecting lever and the latchpawl of the engaging-and-connecting lever is configured to latch ontothe tooth (teeth) or the groove(s) of the catch member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view schematically showing a state before the pedalratio is changed in one example of the embodiment of the brake pedalapparatus according to the invention.

FIG. 2 shows a cross-sectional view (a) taken along a IIA-IIA line inFIG. 1, and a right-side view (b) of FIG. 1.

FIG. 3 schematically shows a state immediately after the pedal ratio hasbeen changed in the brake pedal apparatus of the example shown in FIG.1, wherein (a) is a front view thereof and (b) is an partially enlargedview of (a).

FIG. 4 schematically shows an engaging-and-connecting lever and thecatch member of the brake pedal apparatus of the example shown in FIG.1, wherein (a) is a view showing a state in which anengaging-and-connecting lever and a catch member do not latch eachother, and (b) is a view showing a state in which theengaging-and-connecting lever and a catch member are latched with eachother.

FIG. 5 is a view schematically showing a conventional brake apparatusfor general use.

FIG. 6 schematically shows the brake pedal apparatus disclosed inJP2002-347590, wherein (a) is a front view similar to FIG. 5, and (b) isa partially enlarged view showing a state immediately after the pedalratio has been changed.

FIG. 7 shows the pedal stroke-pedal ratio profile in the brake pedalapparatus of the example shown in FIG. 1 and the brake pedal apparatusdisclosed in JP2002-34590. (a) is a graph that shows the pedal strokepedal ratio characteristics when the engaging means 15 engages to theL-shaped member 43 or the retaining portion 41. (b) is a graph thatshows the pedal stroke pedal ratio characteristics when the engagementof the engaging means 15 with the L-shaped member 43 or the retainingportion 41 is cancelled.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the best mode for carrying out the invention will bedescribed with reference to the drawings.

FIG. 1 is a front view schematically showing a state before the pedalratio is changed in one example of the embodiment of the brake pedalapparatus according to the invention. FIG. 2(a) is a cross-sectionalview taken along a IIA-IIA line in FIG. 1 (a partial cross-sectionalview in which a shaft support portion passes through the center of theshaft). FIG. 2(b) is a right-side view of FIG. 1 (a view from which someof the elements are omitted and that shows a cross section in which theshaft support portion passes through the center of the shaft) FIG. 3schematically shows a state immediately after the pedal ratio has beenchanged in the brake pedal apparatus of this example, wherein (a) is afront view there of and (b) is a partially enlarged view of (a). Itshould be noted that in a brake apparatus equipped with the brake pedalapparatus of this example, the same components as those of the brakeapparatus disclosed in JP-A-2002-347590, shown in the foregoing FIGS. 5,6(a), and 6(b) are designated by the same reference numerals, wherebythe detailed description thereof is omitted.

As shown in FIG. 1, most of the structure of the brake pedal apparatus50 in the brake apparatus 1 of this example is the same as theconventional brake pedal apparatus 50, shown in FIGS. 6(a) and 6(b);therefore, only the structures different from the conventional brakepedal apparatus 50 will be described, the same structures will not beelaborated upon further. Likewise, the structures of the brake apparatus1 other than the structures of the brake pedal apparatus 50 shown inFIG. 1 are not shown as with the brake apparatus 1 shown in FIG. 6(a),the brake apparatus 1 of FIG. 1 is equipped with a MCY 4, WCTs 5, 6, 7,and 8, and a reservoir 9, which are the same as those of the brakeapparatus 1 shown in FIG. 5.

Although the first lever member 2 a ₁ shown in FIGS. 6(a) and 6(b) isformed almost in a linear shape, a first lever member 2 a ₁ in the brakepedal apparatus 50 of this example is formed in an inverted “V”-shape,as shown in FIGS. 1 and 2(a) and 2(b). The inverted “V”-shaped firstlever member 2 a ₁ is pivotably supported by a bracket 10 a at itsangular portion via a first pivot shaft 11, and is relatively pivotablyconnected to the first lever member 2 a ₂ at a position that is aboveand on the left of the first pivot shaft 11, which is at the angularportion of the first lever member 2 a ₁.

The brake pedal apparatus 50 of this example is also equipped with anL-shaped rigid-body member 43 and a torsion spring 44, in place of thearc-shaped rigid-body member 39 and the spring 40 that urges thisarc-shaped member 39 shown in FIGS. 6(a) and 6(b).

The L-shaped member 43 includes a shorter linear portion 43 a and alonger linear portion 43 b, and is pivotably supported on the bracket 10a via the pivot shaft 42 at an angular portion of these linear portions43 a and 43 b. In that case, the longer linear portion 43 b of theL-shaped member 43 is not equipped with the retaining portion 41 shownin FIG. 6(b), which is composed of the V-shaped groove.

Furthermore, the torsion spring 44 is supported on the bracket 10 a, andone end of the torsion spring 44 is secured to the bracket 10 a whilethe other end is securely connected to an end of the longer linearportion 43 b of the L-shaped member 43 (the opposite end to the pivotshaft 42). By the spring force of the torsion spring 44, the L-shapedmember 43 is urged clockwise in FIG. 1 at all times. When the brakepedal apparatus 50 is in an inoperative condition and in a normalcondition (the condition before the pedal ratio change), a pin-shapedengaging means 15 of the first lever member 2 a ₁ is abutted against thesurface of the L-shaped member 43 that opposes the engaging means 15 atthe angular portion of the two linear portions 43 a and 43 b. Theengaging means 15 is configured so as to shift along the linear portion43 b of the angular portion of the L-shaped member 43 with which thecontact angle changes simply and continuously and does not changeabruptly while abutting against it, from the longer linear portion 43 b.The engaging means 15 is abutted against the opposing surface of thelinear portion 43 b at all times, and the spring force of the torsionspring 44 is applied to the engaging means 15 through the L-shapedmember 43 at all times.

One end of a V-shaped engaging-and-connecting lever 45 is pivotablysupported on the other end of the first lever member 2 a ₁, not on theend thereof that is on the engaging member 15 side by a pivot shaft 46.A latched pawl-45 a is formed at one end of the engaging-and-connectinglever 45, as shown in FIG. 4(a). The other end of theengaging-and-connecting lever 45 abuts against the longer linear portion43 b of the L-shaped member 43 when the engaging means 15 of the firstlever member 2 a ₁ is abutting against the angular portion of the linearportions 43 a and 43 b of the L-shaped member 43, as shown in FIG. 1,whereas it disengages from the linear portion 43 b of the L-shapedmember 43 when the engaging means 15 has shifted from the angularportion of the L-shaped member 43 along the linear portion 43 b, asshown in FIG. 3(b). The engaging-and-connecting lever 45 is located at aposition spaced above the shaft 37 when it is abutting against theL-shaped member 43, as shown in FIG. 1. As shown in FIG. 3(a), theengaging-and-connecting lever 45 pivots clockwise in the figure by itsown weight, with the pivot shaft 46 being the center, to abut againstthe shaft 37 when it disengages from the linear portion 43 b of theL-shaped member 43.

As shown in FIGS. 1 and 2(a), the second lever member 2 a ₂ is equippedwith a catch member 47 composed of an arc-shaped plate-like member so asto oppose the latch pawl 45 a. As shown in FIGS. 4(a) and 4(b), on thesurface of the catch member 47 opposing the latch pawl 45 a, apredetermined number of teeth 47 a onto which the latch 45 a can latchis formed. When the engaging-and-connecting lever 45 abuts against theL-shaped member 43, the latch pawl 45 a comes apart from the teeth 47 aand does not latch on these teeth 47 a so that the first lever member 2a ₁ and second lever member 2 a ₂ are not connected with each other, asshown in FIG. 4(a). When the connecting lever 45 disengages from theL-shaped member 43 and pivots by its own weight, the latch pawl 45 alatches onto the teeth 47 a, whereby the first lever member 2 a ₁ andthe second lever member 2 a ₂ are connected with each other and pivotunitarily, as shown in FIG. 4(b).

Although in the foregoing example, two lever members, the third and thefourth lever members 2 a ₄ and 2 a ₅ are provided as the lever membersfor connecting the second lever member 2 a ₂ to the input shaft 3 a, oneor more of any number of lever members may be provided in the invention.

The other structures of the brake apparatus 1 of this example areidentical to the previously-described conventional example.

In the inoperative condition, the thus-configured brake pedal apparatus50 of the brake apparatus 1 of this example is in an inoperativecondition shown in FIG. 1, wherein: the pin-shaped engaging means 15 iskept abutting against the angular portion of the L-shaped member 43 bythe spring force of the torsion spring 44; a stop portion 2 a ₈ abutsonto the first pivot shift 11; and further, the other end of theengaging-and-connecting member 45 (the end opposite the latch pawl 45 a)abuts onto the linear portion 43 b of the L-shaped member 43 so that thelatch pawl 45 a does not latch onto the teeth 47 a of the catch member47.

When the brake pedal 2 is depressed in a normal manner from thisinoperative condition, the pedal force F_(p) does not reach the setvalue F_(p0) and the pedal-ratio change condition is not established;therefore, the first lever member 2 a ₁ does not pivot, as in thepreviously-described conventional example, and the engaging means 15 iskept abutting onto the angular portion of the L-shaped member 43. Thatis, the engagement relation is maintained between the engaging means 15and the L-shaped member 43. Therefore, the L-shaped member 43 does notpivot and the engaging-and-connecting lever 45 is kept in theinoperative condition.

Then, only the second lever member 2 a ₂ pivots clockwise in FIG. 1,with the second pivot shaft 13 being the center. Consequently, the thirdlever member 2 a ₄ pivots counterclockwise via the fourth lever member 2a ₅, with the shaft 37 being the center, and the input shaft 3 a strokesforward, causing the booster 3 to actuate and thus operating a normalbrake. When the brake pedal 2 is released, each of the lever members 2 a₄, 2 a ₅, and 2 a ₂ pivots in an opposite, inoperative direction, andthe brake pedal apparatus 50 enters an inoperative condition shown inFIG. 1, whereby the normal brake is cancelled.

For example, when the brake pedal 2 is depressed more strongly than in anormal brake operation because of emergency braking or the like, thepedal force F_(p) is the set value Fp₀ or higher, that is, thepedal-ratio change condition is established. Consequently, as in thepreviously-described conventional example, the first lever member 2 a ₁pivots clockwise with the first pivot shaft 11 being the center, asshown in FIGS. 3(a) and 3(b). Thereby, the engaging means 15 shifts fromthe angular portion of the linear portion 43 b of the L-shaped member 43while keeping abutment with this linear portion 43 b and causing thisL-shaped member 43 to pivot counterclockwise, cancelling the engagementrelation between the engaging means 15 and the L-shaped member 43.

At this time, the engaging means 15 shifts directly from the linearportion 43 b at the angular portion, abutting to the linear portion 43 bin which the contact angle changes simply and continuously and does notchange abruptly, and therefore, the friction force generated in thecancellation of the engagement relation between the engaging means 15and the L-shaped member 43 is small. Thus, the resistance caused by thefriction force is reduced in the shift of the engaging means 15, thatis, the pivoting of the first lever member 2 a ₁. The engaging means 15smoothly shifts, and few variation or pedal shock occurs when cancelingthe engagement relation between the engaging means 15 and the retainingportion 41, that is, when changing the pedal ratio.

Moreover, since the L-shaped member 43 tends to move away from the otherend of the “V”-shaped engaging-and-connecting lever 45 by thecounterclockwise pivoting of the L-shaped member 43, theengaging-and-connecting lever 45 pivots clockwise in FIG. 1 by its ownweight, with the pivot shaft 46 being the center. When the other end ofthe engaging-and-connecting lever 45 comes apart from the L-shapedmember 43, the engaging-and-connecting lever 45 further pivots by itsown weight, abutting onto the pivot shaft 37 and causing the latch pawl45 a to latch onto the teeth 47 a. That is, at the stage where theengagement relation is cancel-led between the engaging means 15 and theL-shaped member 43, the latch pawl 45 a latches onto the teeth 47 a andthe first lever member 2 a ₁ and the second lever member 2 a ₂ areunified each other.

At this time, the other end of the engaging-and-connecting lever 45abuts against the linear portion 43 b in which the contact angle withthe L-shaped member does not abruptly change only by the own weight ofthe engaging-and-connecting lever 45, and the engaging-and-connectinglever 45 pivots only by its own weight when the other end of theengaging-and-connecting lever 45 disengages from the linear portion 43b; therefore, there is little resistance in the pivoting of theengaging-and-connecting lever 45, and the latching between the latchpawl 45 a and the teeth, 47 a is performed smoothly. Consequently, fewvariation or pedal shock occurs at the time of the latching between thislatch pawl 45 a and the teeth 47 a.

Moreover, the latching between the latch pawl 45 a and the teeth 47 a isachieved before the first lever member 2 a ₁ abuts onto the stop portion2 a ₈ of the pivot shaft 11. Then, the pedal ratio is changed byunification of the two lever members 2 a ₁ and 2 a ₂.

Furthermore, the second lever member 2 a ₂ also pivots in the samedirection, with a connecting shaft 2 a ₇ being the center, and at thistime, the first lever member 2 a ₁ and the second lever member 2 a ₂tend to shift toward a balanced position, as in the foregoingconventional example. However, since the latch pawl 45 a latches ontothe teeth 47 a so that the first lever member 2 a ₁ and the second levermember 2 a ₂ are unified with each other as discussed above, the firstpivot shaft 11 does not abut directly on the stop portion 2 a ₈, whichis away from the first pivot shaft 11.

Consequently, when the first lever member 2 a ₁ and the second levermember 2 a ₂ are unified, little contact noise is produced. Whenconsidering the shift of the first lever member 2 a ₁ and the secondlever member 2 a ₂ to the balanced position after the cancellation ofthe engagement relation between the engaging means 15 and the L-shapedmember 43 with respect to the pedal ratio change, the pedal ratiochanges from a pedal ratio before the pedal ratio change to a pedalratio at the time when the latch pawl 45 a latches onto the teeth 47 aand the first lever member 2 a ₁ and the second lever member 2 a ₂ areunified. This pedal ratio at the time when the latch pawl 45 a latchesto the teeth 47 a results nearly in a desired pedal ratio since there isfew relative shift between the first lever member 2 a ₁ and the secondlever member 2 a ₂. Therefore, even when the pedal ratio is changed, fewpedal shock occurs.

The pedal ratio that is changed by the unification of the first levermember 2 a ₁ and the second lever member 2 a ₂ results in a large pedalratio. That is, the MCY pressure is made to have so-called inversetwo-stage characteristics, wherein, as the pedal force F_(p) increases,the MCY pressure increases at a larger boosting ratio than theconventional boosting ratio.

In addition, even in a boosting power failure by the booster 3, thepedal ratio is changed likewise and is made large when the pedal forceF_(p) is the pedal force F_(pa) or higher, which is a set value F_(p0).Therefore, the MCY pressure linearly increases at a considerably greatervalue than it increases conventionally, in accordance with the increasedpedal ratio so that the braking force is assisted.

The pedal stroke-pedal ratio profile of the brake pedal apparatus 50 inthis example results in the same profile as the foregoing profile shownin FIG. 7(a) when the latch pawl 45 a of the engaging-and-connectinglever 45 does not latch onto the teeth 47 a of the retaining member-47,whereas it results in the same profile as the profile shown in the FIG.7(b) when the latch pawl 45 a latches onto the teeth 47 a of theretaining member 47.

In the brake pedal apparatus 50 in this example, the resistance causedby the shift of the engaging means 15 is reduced at the time ofcancellation of the engagement relation between the engaging means 15and L-shaped member 43 when changing the pedal ratio; therefore, theengaging means 15 can be shifted smoothly, and both variation and pedalshock can be suppressed in the cancellation of the engagement relationbetween the engaging means 15 and the retaining portion 41. Moreover,the contact noise generated at the time of the unification of the firstlever member 2 a ₁ and the second lever member 2 a ₂ can be prevented.Furthermore, since the pedal ratio at the time of the unification of thefirst lever member 2 a ₁ and the second lever member 2 a ₂ can be madenearly a desired pedal ratio, the pedal shock associated with thechanging of the pedal ratio can be prevented.

Thus, the brake pedal apparatus 50 of this example makes it possible toobtain a better pedal feel in changing the pedal ratio than in theconventional example.

Moreover, since the latch pawl 45 a of the engaging-and-connecting lever45 latches onto the teeth 47 a of the retaining member 47, the pedalratio can be changed with a simple structure.

Furthermore, because the torsion spring 44 is adopted as the spring forurging the L-shaped member 43, it requires smaller space to install incomparison with the coil spring in the previously-mentioned conventionalexample.

The other operations and advantages of the brake apparatus 1 of thisexample are the same as those of the foregoing brake apparatus 1 of theconventional example.

It is also possible to employ other latching means such as a groove, inplace of the teeth 47 a of the retaining member 47. In place of thelinear portion 43 b of the L-shaped member 43, an arc-shaped portion maybe formed. In that case, it is desirable that the radius of curvature ofthe arc-shaped member should be relatively large.

In addition, although the brake pedal apparatus 50 in each of theexamples adopts the negative booster 3, it is possible to use a boosteror a pressure source that uses other power sources, such as liquidpressure or air pressure.

Further, although each of the foregoing examples uses the booster 3, itis not necessary to use the booster 3 and it is also possible to connectthe input shaft of the master cylinder 4 (for operating the piston ofthe master cylinder 4) directly to the second lever member 2 a ₂.

INDUSTRIAL APPLICABILITY

The brake pedal apparatus according to the invention can be suitablyapplied to the brake pedal apparatus of the brake apparatus for vehiclessuch as automobiles.

1. A brake pedal apparatus comprising: a first lever member whose midportion is pivotably supported on a vehicle body by a first pivot shaft;a second lever member having a pedal on an end thereof and beingrelatively pivotably connected to an end of the first lever member by asecond pivot shaft, to which an input shaft of a booster or of a mastercylinder is pivotably coupled; a pivot-inhibiting control means forcontrolling pivoting of the first lever member so that the first levermember is inhibited from pivoting when a predetermined condition is notestablished while the first lever member is permitted to pivot when thepredetermined condition is established; and a joining means for causingthe second lever member to pivot together with the first lever member,with the first pivot shaft being a pivot center, when the first levermember is permitted to pivot, the brake pedal apparatus characterized inthat: the pivot-inhibiting control means comprises an engaging meansprovided on the first lever member, and a shift-inhibiting control meanshaving an abutting surface onto which the engaging means abuts and beingfor inhibiting the engaging means from shifting so as to keep itsengagement with the engaging means when the predetermined condition isnot established, and for permitting the engaging means to shift so as tocancel its engagement with the engaging means when the predeterminedcondition is established and the abutting surface of theshift-inhibiting control means is an abutting surface whose shape doesnot change abruptly.
 2. The brake pedal apparatus as set forth in claim1, characterized in that: the joining means includes a catch memberprovided on the first lever member and a connecting member provided onthe second lever member and being latchable onto the catch member andthe connecting member is configured to be controlled by theshift-inhibiting control means so that it does not latch onto the catchmember when the predetermined condition is not established while itlatches onto the catch member when the predetermined condition isestablished.
 3. The brake pedal apparatus as set forth in claim 2,characterized in that: the catching member has a predetermined number oftooth (teeth) or groove(s), and the connecting member is providedpivotably on the second lever member and includes anengaging-and-connecting lever having a latch pawl being latchable withthe tooth (teeth) or the groove(s) and the engaging-and-connecting leveris controlled by the shift-inhibiting control means so that theengaging-and-connecting lever is set at a position such that the latchpawl does not latch with the tooth (teeth) or groove(s) when thepredetermined condition is not established, while theengaging-and-connecting lever is set at a position such that the latchpawl latches with the tooth (teeth) or groove(s) when the predeterminedcondition is established.